<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .goBack{
            width: 200px;
            height: 50px;
            background-color: blue;
            text-align: center;
            line-height: 50px;
            color: #fff;
            position: fixed;
            right: 20px;
            bottom: 50px;
        }
    </style>
</head>
<body>
    <div id="top" style="height: 2000px;">ndkdnksdmcvksdlvnkl</div>
    <div class="goBack">
        <a href="#top">返回页面顶部</a>
    </div>
</body>
</html>